scale.yml failed because variables are overrided by roles/kubespray-defaults/defaults/main.yaml

[snowmansora]

Environment:
Kubespray version (commit) (git rev-parse --short HEAD):
b7c2265
Network plugin used:
Flannel

When trying to add a new node via scale.yml, it failed at:

TASK [network_plugin/calico : Calico | Copy calicoctl binary from download dir] *************************************************************************************************************************************************************
fatal: [k8s-1]: FAILED! => {"changed": false, "msg": "Source /tmp/releases/calicoctl not found"}
fatal: [k8s-2]: FAILED! => {"changed": false, "msg": "Source /tmp/releases/calicoctl not found"}
fatal: [k8s-3]: FAILED! => {"changed": false, "msg": "Source /tmp/releases/calicoctl not found"}

I set kube_network_plugin to flannel in my group_vars, so calico tasks should never run and fail.
After troubleshooting, kube_network_plugin is set to calico because of:

kubespray/scale.yml

Line 72 in b7c2265

include_vars: roles/kubespray-defaults/defaults/main.yaml

I think this is a bug because variables in roles/kubespray-defaults/defaults/main.yaml are not supposed to have such "high precedence", so it should never be used with include_vars.